Glycine

Some interesting facts about glycine:

Glycine can be a conditionally essential amino acid
While glycine is not an essential amino acid most of the time (essential amino acids are required in the diet as the body cannot manufacture them), there are certain special circumstances which makes it conditionally essential; this means glycine becomes an essential amino acid under special conditions, especially when intake of the essential amino acid serine and threonine are very low.
The amino acids serine and threonine are used to make glycine
The body uses the non-essential amino acid serine and the essential amino acid threonine to synthesise glycine.

While glycine is not an essential amino acid most of the time, there are certain special circumstances which makes it conditionally essential

Glycine functions as a building block of protein in the body
Glycine, just like all the other amino acids, is one of the building blocks of all proteins in the body, which not only include muscles, but also all the other proteins required for normal function of the body.